1. Field of the Invention
The invention relates to data processing systems and more particularly to a method and apparatus for connecting a workstation to a local area network over a media link.
2. Description of the Related Art
A Local Area Network, or LAN, is a data communications system which allows a number of independent devices to communicate with each other within a moderately-sized geographical area. The term LAN is used to describe networks in which most of the processing tasks are performed by a workstation such as a personal computer rather than by the shared resources.
A LAN consists of a desktop workstation which performs processing tasks and serves as the user's interface to the network, wiring system which connects the workstations together, and a software operating system which handles the execution of tasks on the network.
The physical line which connects the components of a LAN, is called the network medium. The most commonly used media are wire, cable, and fiber optics. Coaxial cable is the traditional LAN medium and is used by Ethernet.TM., the most widely recognized standard. The newest LAN transmission medium is fiber-optic cable which exhibits a superior performance over any of the other media.
There is an increasing need for high-performance-internode communication. The mainframe computer is being extended or replaced by department computers, workstations, and file servers. This decentralization of computers increases the amount of information that needs to be transferred between computers on a LAN. As computers get faster, they handle data at higher and higher rates.
In the above-referenced application Ser. No. 07/291,700 there is described a Local Area Network architecture based on an active star topology. Nodes attach to the hub of the star through duplex communication links. Messages transferred between nodes are passed through the hub, which is responsible for arbitration and routing of messages. Unlike the prior bus topology, or ring topology, each node of the active star responds only to those messages that are intended for it. Routing of messages is accomplished by a destination address in the header of the message. These addresses are unique to each node and provide the means by which the hub keeps the communication between nodes independent.
The active star configuration has the advantage that it increases network bandwidth. In typical networks the performance of the node interface to the network is only equivalent to the network bandwidth. This is because messages can be transferred only at the rate of the media used as the link interface from the node to the network, and the fact that only one message can be transferred at a time. Ethernet, Star Lan, FDDI, all exhibit this characteristic as they are essentially broadcast buses, in which every node has every other node's message traffic passing through it.
There is also the problem of being able to mix existing nodes that operate at relatively low speeds with more advanced nodes that operate at higher speeds.